AM335x Linux Framebuffer

In your first post you refer to this wiki: http://processors.wiki.ti.com/index.php/Linux_Core_LCD_Controller_User_Guide Please read it carefully. There are two types of display support - DRM and fbdev. For framebuffer support you need to configure the driver as described in the fbdev section.

Thank you, that helps clear things up a bit.  Unfortunately the frame buffer is still not showing up in the dev folder.

I downgraded to 4.1.6 so I should now be running the supported kernel.

I have added the following to my config file (omap2plus_defconfig) : 

CONFIG_FB_DA8XX=y
CONFIG_FB_DA8XX_TDA998X=y

My dts file is as follows:

/*
 * Copyright (C) 2012 Texas Instruments Incorporated - http://www.ti.com/
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
/dts-v1/;

#include "am33xx.dtsi"
#include "am335x-bone-common.dtsi"

/ {
	model = "TI AM335x BeagleBone Black";
	compatible = "ti,am335x-bone-black", "ti,am335x-bone", "ti,am33xx";
};

&ldo3_reg {
	regulator-min-microvolt = <1800000>;
	regulator-max-microvolt = <1800000>;
	regulator-always-on;
};

&mmc1 {
	vmmc-supply = <&vmmcsd_fixed>;
};

&mmc2 {
	vmmc-supply = <&vmmcsd_fixed>;
	pinctrl-names = "default";
	pinctrl-0 = <&emmc_pins>;
	bus-width = <8>;
	status = "okay";
};

&am33xx_pinmux {
	nxp_hdmi_bonelt_pins: nxp_hdmi_bonelt_pins {
		pinctrl-single,pins = <
			0x1b0 0x03      /* xdma_event_intr0, OMAP_MUX_MODE3 | AM33XX_PIN_OUTPUT */
			0xa0 0x08       /* lcd_data0.lcd_data0, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xa4 0x08       /* lcd_data1.lcd_data1, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xa8 0x08       /* lcd_data2.lcd_data2, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xac 0x08       /* lcd_data3.lcd_data3, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xb0 0x08       /* lcd_data4.lcd_data4, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xb4 0x08       /* lcd_data5.lcd_data5, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xb8 0x08       /* lcd_data6.lcd_data6, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xbc 0x08       /* lcd_data7.lcd_data7, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xc0 0x08       /* lcd_data8.lcd_data8, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xc4 0x08       /* lcd_data9.lcd_data9, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xc8 0x08       /* lcd_data10.lcd_data10, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xcc 0x08       /* lcd_data11.lcd_data11, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xd0 0x08       /* lcd_data12.lcd_data12, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xd4 0x08       /* lcd_data13.lcd_data13, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xd8 0x08       /* lcd_data14.lcd_data14, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xdc 0x08       /* lcd_data15.lcd_data15, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT | AM33XX_PULL_DISA */
			0xe0 0x00       /* lcd_vsync.lcd_vsync, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT */
			0xe4 0x00       /* lcd_hsync.lcd_hsync, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT */
			0xe8 0x00       /* lcd_pclk.lcd_pclk, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT */
			0xec 0x00       /* lcd_ac_bias_en.lcd_ac_bias_en, OMAP_MUX_MODE0 | AM33XX_PIN_OUTPUT */
		>;
	};
	nxp_hdmi_bonelt_off_pins: nxp_hdmi_bonelt_off_pins {
		pinctrl-single,pins = <
			0x1b0 0x03      /* xdma_event_intr0, OMAP_MUX_MODE3 | AM33XX_PIN_OUTPUT */
		>;
	};
};

&i2c0 {
	hdmi1: hdmi@70 {
		compatible = "nxp,tda998x";
		reg = <0x70>;
	};
};

&lcdc {
	hdmi = <&hdmi1>;
	display-timings {
		clock-frequency = <65000000>;
		hactive = <1024>;
		vactive = <768>;
		hback-porch = <220>;
		hfront-porch = <40>;
		vback-porch = <21>;
		vfront-porch = <7>;
		hsync-len = <60>;
		vsync-len = <10>;
		de-active = <1>;
		pixelclk-active = <1>;
	};
};

Hi,

Please build your kernel with tisdk_am335x-evm_defconfig. The omap2plus_defconfig file is suitable for multicore devices like OMAP4/5, etc...

Also do not add the CONFIG_FB_DA8XX=y & CONFIG_FB_DA8XX_TDA998X=y options. They will mess with the existing drm driver. Use the default (unmodified) configuration, and you should be able to work with dev/fb0.

Here is the output from my Starter Kit, running kernel 4.1.6 with DRM driver:

root@am335x-evm:/dev# cat /dev/urandom > /dev/fb0                                                              

cat: write error: No space left on device    

And the screen of the starter kit gets the random pixels displayed, see attached image:

I am also able to work with all the entries in root@am335x-evm:/sys/class/graphics/fb0

Best Regards,

Yordan